Measuring system and method for the functional monitoring thereof

ABSTRACT

A measuring system includes a measuring device, another device and a device configured to transmit data enabling bits of data to be transmitted between the measuring device and the other device. The measuring device also includes a signal monitoring circuit and a switch element. The switch element is electrically contacted to a test potential source. The test potential source is in contact with the signal monitoring circuit according to a switch element state. The signal monitoring circuit is also in contact with the device for transmitting date. A method provides for functional monitoring of such a measuring system in a monitoring mode when a test potential is applied.

FIELD OF THE INVENTION

The present invention relates to a measuring system, e.g., aposition-measuring system, the functioning of which may be simple totest. The present invention is also directed to a method for testing forcorrect functioning.

BACKGROUND INFORMATION

In position-measuring systems, position sensors in a measuring devicegenerate electrical signals, which provide information on the positionof objects which are moving in relation to one another. The presentinvention relates to measuring systems that use measuring devices whichproduce comparatively precise, incremental positional information, aswell as relatively rough positional information. These two types ofpositional data may be of particular importance for controlling theelectric drives used in moving the axes of a processing machine, such asof a machine tool or robot. In such applications, the precise,incremental, positional information may be used to precisely determinepositions, for example, of a tool of a machine tool.

Such electric drives may be arranged as rotary electromotors, for whichrotary transducers may be used to perform angle-of-rotationmeasurements. Example embodiments of the present invention may also beused in connection with the operation of linear motors.

Rotary transducers may enable angular position measurements to be takenon a rotatable shaft in incremental measuring steps. However, so-calledabsolute-value encoders, also described as rotary, shaft-angle orincremental encoders, are also conventional. These permit an absoluteangular determination to be made within one single shaft rotation.Moreover, if the need arises to determine the number of completed shaftrotations, then so-called multiturn rotary encoders may be used. Suchmultiturn rotary encoders determine the absolute angular position withinone shaft rotation, i.e., between 0° and 360°, using an encoder diskwhich is connected to the shaft and is scanned by a suitablephotoelectric scanning unit. Thus, it is also possible to measure theabsolute position of the driven shaft over a plurality of rotations.

The signals of these measuring devices may be used for controlling theprocessing machines. The term processing machine is not limited tomachine tools, but also includes machines for populating electroniccomponents or for machining semiconductor elements. Automation orprogrammable machines, such as robots, also fall under theprocessing-machine designation.

In conventional position-measuring systems, in addition to the digitalpositional data, analog position signals are also transmitted from themeasuring device to the machine control, where these signals are theninterpolated. Due to the advancing miniaturization of electronics, theseinterpolation processes are being increasingly carried out in a suitableelectronic circuit within the measuring device itself, so that theanalog position signals are not transmitted to the machine control. Thismay reduce the outlay for wiring, which may have a significant effect onthe costs of a measuring system.

However, in safety-related machine applications under conventionalmethods, the digital positional data and the analog position signals arecompared in the machine control in order to detect errors. However,since analog position signals may be missing in the machine control, itmay no longer be possible for this comparison to be made.

Therefore, in measuring systems, in which no analog position signalsarrive in the machine control for the mentioned reasons, besides thecurrent, often absolute positional data, it may not be unusual forso-called static bits to be transmitted via a parallel or serialinterface from the measuring device to the machine control. These staticbits may be error bits, for example, which, in normal operation, alwaysexhibit a specific level, and only in a (very rare) case of error, pointto an error due to a change in level.

This manner of transmitting error information may be disadvantageous,e.g., in the case of safety-related monitoring, because it may not beruled out that a defect may cause a constant level of an error bit tocontinually be output, thus that this defect does not permit a change inlevel even in the case of faults or malfunctions.

German Published Patent Application No. 38 29 815 of the assignee hereofdescribes a position-measuring device or position transducer, where atest for errors is initiated by an activation signal. However, theperformance reliability of the monitoring electronics itself may not bechecked. Moreover, the outlay entailed for signal transmission may becomparatively large.

SUMMARY

According to an example embodiment of the present invention, a measuringsystem is provided which may render possible a safe and reliableoperation of processing machines, the outlay for signal transmissionbeing comparatively low.

Moreover, according to an example embodiment of the present invention, amethod for checking error information may significantly enhance thesafety and reliability of processing machines.

A fault may be able to be induced, in a deliberate, controlled manner,in the measuring device during a test operation, and it is then checkedby applying a test potential, whether an error bit having acorresponding level arrives in the machine control. Example embodimentsof the present invention may enable the performance reliability of amonitoring electronics, e.g., of a signal-amplitude monitoring circuitto be checked. The test potential may be understood, for instance, to bethe voltage of a test potential source or, in a simple case, the earthpotential.

In an example embodiment of the present invention, the circuit statesfor connecting to the test potential source, e.g., automatically, aretriggered by the machine control.

According to an example embodiment of the present invention, a measuringsystem includes: a measurement device; a second device; and adata-transmission device configured to transmit data bits between themeasurement device and the second device. The measurement deviceincludes a signal-monitor circuit and a control element, the controlelement in electrical contact with a test potential source. In acircuit-element state, the test potential source is in contact with thesignal-monitor circuit and the signal-monitor circuit is in contact withthe data-transmission device.

According to an example embodiment of the present invention, a methodfor testing a measuring system for correct functioning includes: in anormal operation of the measuring system, transmitting, by a measurementdevice to a second device via a data-transmission device, a bit having aconstant level to signal a fault-free operation of the measuring device;and in a test operation of the measuring system: electrically contactinga signal-monitoring circuit of the measuring device with atest-potential source; and in the second device, checking whether thetest operation effects a change in a level of the bit in relation to thelevel of the bit in the normal operation.

According to an example embodiment of the present invention, a measuringsystem includes: measuring means; second means; and data-transmittingmeans for transmitting data bits between the measuring means and thesecond means. The measuring means includes signal-monitoring circuitmeans and control element means, the control element means in electricalcontact with a test potential source means. In a circuit-element state,the test potential source means is in contact with the signal-monitoringcircuit means and the signal-monitoring circuit means is in contact withthe data-transmitting means.

Further aspects and features of the measuring system and of acorresponding method, as well as details pertaining thereto, aredescribed below with reference to the appended Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic view of a measuring system according to anexample embodiment of the present invention in normal operation.

FIG. 1 b is a schematic view of a measuring system according to anexample embodiment of the present invention in test operation.

FIG. 2 is a voltage curve when a test voltage is used.

FIG. 3 is a schematic representation of a measuring system according toan example embodiment of the present invention.

DETAILED DESCRIPTION

In FIG. 1 a, a measuring system is illustrated, which includes a rotarytransducer 1, a machine control 2, and a data-transmission device 3.

Rotary transducer 1 has photoelements 1.1, 1.2, amplifiers 1.3, 1.4, anevaluation electronics 1.5, and a signal-amplitude monitoring circuit1.6. Arranged at the lines between amplifiers 1.3, 1.4 and evaluationelectronics 1.5, are branch lines having resistors 1.7, 1.8. Disposedabove that in the circuit of rotary transducer 1 are control elements1.9, 1.10, which electrically contact a test potential source 1.11.

Control elements 1.9, 1.10 may assume two control element states. In thefirst control element state, test potential source 1.11 is isolated fromsignal-amplitude monitoring circuit 1.6, and in the second controlelement state, an electrical contact is established between testpotential source 1.11 and signal-amplitude monitoring circuit 1.6.

Data-transmission device 3 includes an interface socket 3.1 at rotarytransducer 1, a multicore cable 3.3 having plug connectors, and aninterface socket 3.1 at machine control 2. Alternatively thereto, awireless data-transmission device 3 may also be provided.Correspondingly, suitable transmitter and receiver elements may beprovided in place of interface sockets 3.1, 3.2.

In accordance with the angular position of a shaft to be measured, lightfrom an LED is modulated and converted by photoelements 1.1, 1.2 intophotoelectric currents. These photoelectric currents are amplified withthe aid of amplifiers 1.3, 1.4, so that the result is analog positionsignals, which have a sinusoidal form, as in accordance with FIG. 2.These position signals are fed in evaluation electronics 1.5, interalia, to an interpolation process, thereby enabling the angular orpositional resolution of measuring device 1 to be greatly increased.Moreover, in evaluation electronics 1.5, absolute digital positionalvalues are generated, which, in the illustrated example, are transferredas a data packet, which includes a multiplicity of data bits, seriallyvia interfaces 3.1, 3.2 and cable 3.3 to the machine control in a cycletime of 50 μs.

In parallel thereto, the analog position signals are fed to asignal-amplitude monitoring circuit 1.6. It is checked in thissignal-amplitude monitoring circuit 1.6 whether the amplitudes of theanalog position signals are within plausible limits. In normaloperation, this criterion is met by the analog position signals, so thatthe same data packet used to transmit the absolute digital positionalvalues to machine control 2 is also used to transmit an error bit, whoselevel signals or indicates the normal state, i.e., the fault-freeoperation of the measuring system. Thus, this error bit is typicallytransmitted at a constant level, in the exemplary embodiment presentedhere, every 50 μs, from measuring device 1 to machine control 2 and is,therefore, described as a static error bit.

As soon as the amplitudes of the analog position signals are outside ofthe plausible limits, the level of the error bit is changed, and thecorresponding error bit is transmitted to machine control 2 via the nextdata packet. In reaction thereto, machine control 2 triggers anemergency shutoff for the entire machine.

The situation may also arise, however, where the level of the error bitis not able to be changed, for example, due to a short circuit. Then, inspite of a fault, the same error bit level is relayed to machine control2, with the result that the machine would not be shut down, even inresponse to a fault.

To avoid such a danger, a test operation is carried out for a shortduration using a control element state, as illustrated in accordancewith FIG. 1 b. For this purpose, a signal is dispatched by machinecontrol 2 to the measuring device. The signal is transmitted in the formof a code word, or mode command, by machine control 2 via a data line ofcable 3.3 to rotary transducer 1. The data line of cable 3.3 is usedboth for transmitting the mode commands from machine control 2 to rotarytransducer 1, as well as for transmitting data and signals, includingthe error bit, from rotary transducer 1 to machine control 2. Thus, asindicated by the double arrow in FIGS. 1 a, 1 b, and 3, it is a questionof a bidirectional data transmission between machine control 2 androtary transducer 1.

The transmitted mode command is decoded in rotary transducer 1, so thatthe test operation is triggered, which initially results in closing ofcontrol elements 1.9, 1.10. Thus, voltage U_(o) of test-potential source1.11 is supplied to signal-amplitude monitoring circuit 1.6. The levelof voltage U_(o) is derived from the voltage curve of the correspondinganalog position signal (corresponds to the axis of symmetry of thevoltage curve of the analog position signal) in accordance with FIG. 2.As illustrated in FIG. 1 b, resistors 1.7, 1.8 substantially preventvoltage U_(o) from being induced in evaluation electronics 1.5. Thus,given a closed control element 1.9, signal-amplitude monitoring circuit1.6 ascertains that the amplitude of the analog position signal isinsufficient and, therefore, outputs an error bit having a changedlevel. Machine control 2 is programmed such that, during three cycletimes, thus, in this case 150 μs, following injection of voltage U_(o),no reaction (emergency off) is triggered in response to the receipt ofan error bit having a changed level.

However, should no level change in the error bit be ascertained bymachine control 2, although voltage U_(o) had been injected, then anerror message indicating the same is output. In this manner, it ispossible, for example, to test signal-amplitude monitoring circuit 1.6for correct functioning.

In an example embodiment of the present invention, illustrated in FIG.3, a digital signal-amplitude monitoring circuit 1.12 is additionallyintegrated in evaluation electronics 1.5. It carries out a plausibilitycontrol of the digitized positional data in parallel to signal-amplitudemonitoring circuit 1.6. In normal operation, an emergency-off istriggered, as soon as an error bit having a changed level arrives inmachine control 2, regardless of whether it comes from signal-amplitudemonitoring circuit 1.6 or from digital signal-amplitude monitoringcircuit 1.12. An emergency-off also follows when both signal-amplitudemonitoring circuits 1.6, as well as digital signal-amplitude monitoringcircuit 1.12 signal an error via an error bit having a changed level.

If at this point in test operation, signal-amplitude monitoring circuit1.6 is tested for correct functioning by applying test potential U_(o),then machine control 2 may be programmed not to trigger an emergency-offin response to the receipt of an error bit having a changed level fromsignal-amplitude monitoring circuit 1.6. However, if error bits having achanged level, thus quasi two error messages, from both signal-amplitudemonitoring circuit 1.6 and from digital signal-amplitude monitoringcircuit 1.12, reach machine control 2 in test operation, then anemergency-off is triggered. In this manner, a sufficient level ofreliability may be provided in test operation as well.

It should be understood that the present invention is not limited tomeasuring systems and methods for monitoring position signals generatedby photoelements 1.1, 1.2. Rather, temperature signals,frequency-describing signals, or signals which provide information aboutthe charge condition of batteries, etc., may be considered.

Example embodiments of the present invention may be used forposition-measuring devices, which, besides positional data, transmitadditional measuring data from other sensors via a shared interface orvia the shared data-transmission device 3, bidirectionally between theposition-measuring device, in this case rotary transducer 1 and machinecontrol 2. Thus, for example, in addition to positional measurements inrotary transducer 1, speed and/or velocity measurements are also oftentaken using a Ferraris sensor, for example. The performance reliabilityof the signal monitoring of these sensors may also be tested usingexample embodiments of the present invention. The same also applies torotary transducer 1, in which a temperature-monitoring circuit, forexample, for an electromotor, is integrated. The performance reliabilityof the temperature-signal monitoring may also be tested using exampleembodiments of the present invention.

1. A method for testing a measuring system for correct functioning,comprising: in a normal operation of the measuring system, transmitting,by a measurement device to a second device via a data-transmissiondevice, a bit having a constant level to signal a fault-free operationof the measuring device; in a test operation of the measuring system:electrically contacting a signal-monitoring circuit of the measuringdevice with a test-potential source; and in the second device, checkingwhether the test operation effects a change in a level of the bit inrelation to the level of the bit in the normal operation; and outputtingtest data conditional upon a determination that the change has not beeneffected.
 2. The method according to claim 1, wherein in the normaloperation of the measuring system a change in the level of the bittriggers a reaction in the second device, in the test operation, thechange in the level of the bit does not trigger any reaction in thesecond device.
 3. The method according to claim 1, further comprisingelectrically contacting the test-potential source and thesignal-monitoring circuit in response to a signal from the seconddevice.
 4. The method according to claim 1, further comprisingautomatically triggering the test operation in defined time intervals totest the measuring device for correct functioning.
 5. The methodaccording to claim 1, further comprising manually triggering the testoperation to test the measuring device for correct functioning.
 6. Themethod according to claim 1, further comprising automatically triggeringthe test operation to test the measuring device for correct functioningin response to specific machine states being reached.
 7. The methodaccording to claim 6, wherein the specific machine states includes atleast one of (a) a tool change and (b) a workpiece change.
 8. The methodaccording to claim 1, wherein the test data is generated in the testoperation of the measuring system, in the second device, and isindicative of a result of the checking.